Protection of columbium against oxidation

ABSTRACT

Columbium is provided with a barrier on the surface thereof by forming an oxide layer of columbium, complexing the oxide layer with a Group III metal, and then oxidizing the Group III metal, for example, by treatment with phosphoric acid.

United States Patent 1191 Kanter 5] Apr. 9, 1974 PROTECTION OF COLUMBIUM AGAINST 3.057.048 10/1962 Hirakis....- 29/194 OXIDATION 1 3,205,090 9/1965 Caplow .i 1 17/1 13 3,219,474 1 H1965 Priceman' et a1 1 17/71' M [76] Inventor: Jerome J. Kanter, 12300 Hobart 3,318,246 5/1967 Wilhelm et a1. 117/127 x Ave.,'Pa10s Park, 111. 60464 3,362,842 l/1968 Kramer 117/71 3,700.50 10 972 K 1 8 6. 5 R 221 Filed: Feb. 7, 1972 5 I 4 l 7 [211 No 224,25 Primary Examiner-Ralph S. Kendall Related US. Application Data Attorney, Agent, or Firm-Henry L Brinks [63] Continuation-impart of Ser. No. 824,255, May 13,

e 1969, abandoned.

52 -U.s. c1 148/63, 117/127, l48/6.l5 R [57] ABSTRACT [51] II!!- Cl. C23f 7/02 Columbiumis p d with a barrier on the surface [58] Fleld of Search 148/631, 6.15 R, 6.15 2; 4thereofby forming an Oxide layer of colum'biuma 69 plexing theoxide layer with a Group I11 metal, and then oxidizing the Group III metal, for example, by [56] References treatment with phosphoric acid.

UNITED STATES PATENTS 3,038,817 6/1962 Day et a1. 117/705 x 13 Claims, No Drawings PROTECTION OF COLUMBIUM AGAINST OXIDATION This application is a continuation-in-part of application Ser. No. 824,255, filed May 13, 1969 now abandoned.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION Columbium (also known as niobium) possesses many significant properties which make it desirable for many uses. It has a high melting point (4,380 F.), which makes it desirable as a material of construction, such 8 as in jet and diesel engines, gas turbines, dies for high temperature metal working, high temperature reactors, atomic power reactors, and the like. Its low neutroncapture cross section makes it a desirable material for atomic power reactors. Its corrosion resistance and mechanical characteristics also make it a desirable material for many potential uses. It is electrically superconductive at low temperatures.

Among its disadvantages, is the catastrophic oxidation that occurs at temperatures above 1,000 F. At these high temperatures the columbium is consumed by oxidation forming a loose, non-adherent film on the surface. This oxidation problem has limited the application of columbium to uses forwhich it would be otherwise well suited.

In an effort to solve the serious oxidation problem, various alloys of columbium have been prepared. .(See for example U.S. Pat. Nos. 2,838,395, and 2,922,714).

While the alloys of columbium achieve resistance to,

oxidation, the ductility of the metal and mechanical properties are sacrificed.

' The ductility of columbium is markedly influenced- 'erties. Metal alloys also reduce its ductility.

At thepresent time, however, in spite of its desirable properties, only limited amounts of columbium metal are used commercially, although there had been extensive research programs directed to its development for high temperature service. There has been no important expansion on the market.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to It is a further object of the present invention to provide a columbium metal article which is suitable for high temperature service under oxidizing conditions.

It is a further object of the present invention to provide a method for protecting columbium against catastrophic oxidation.

It is still a further object of the present invention to provide a surface barrier for columbium.

It is still yet a further object of the invention to-providean electrically insulative surface for columbium metal.

Other and further objects will be apparent from a re-' view of the specification and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Briefly stated, the present invention is directed to the formation of a layer or barrier on columbium. The.

' layer or surface is resistant to oxidation and/or electri-, cal conduction. The barrier, for example, reduces oxidation at high temperatures, such as temperatures above l,O0O F., 'and yet permits the metal to retain its desirable mechanical properties. The layer also provides electrical insulation that is serviceable under a wide range of temperatures.

The metal to be protected may be pure columbium (also known as niobium), or columbium base metal alloys. The columbium base metal alloys may comprise alloys of tantalum, or the various alloys of aluminum, the latter of which are disclosed in U.S. Pat. Nos.

invention, lesser amounts of alloying constituents are neededfor oxidation resistance with .the result of enhancement of toughness, ductility, formability, and shock resistance.

The surface of the columbium article is provided with an adherent oxide layer. The adherent oxide layer can be accomplished by heating the article in an atmosphere containing oxygen to temperatures in the range y from about 600 F. to about l,200 'F. Lower'tempera tures and longer time exposures to oxygen can also form thedesired adherent film. The columbium oxidelayer is firmly adherent if the oxidation step is performed under the foregoing conditions. The oxidation step may be performed by heating in the above temperature ranges in air. Alternatively, the operation may be performed in special oxidizing atmospheres. The temperatures and the time of oxidation is sufficient-toform provide a process for improving the utility of columan adherent columbium oxide film on the metal without the formation of a loose non-adherent film.

. After the formation of the columbium oxide film, said oxide film is; treated with at least one Group III metal. The Group III metal may be aluminum, scandiurn', yttrium, orthe rareearth metals. The Group III metal may be reacted in solid form with the columbiummetal oxide layer. This may be accomplished by frictionally contacting on the surface of the oxide metal ate a reaction between the columbium metal oxide layer and the aluminum. v

The Group lll metal is applied in solid form to the oxide layer. Usually ambient temperature are adequate for reaction of Group III metal in solid phase with the oxide layer, but in certain instances elevated temperatures may be desirable, and, in any event, the temperatures must be maintained in a range in which the oxide layer will not spall off by the heating. Broadly, the Group III metal is reacted in solid form with the columbium oxide layer in temperatures ranging from ambient to about 1,200 F.

A series of Group III metals may be reacted with the columbium metal oxide layer. For example, it may be desirable first to apply aluminum, and next to apply yttrium metahor one of the rare earth metals, to the columbium oxide layer. ,Yttriurn and rare earth metals are reacted with the columbium metal oxide surface as powders. Because the powdered forms of the yttrium and rare earth metals arepyrophoric, they must be handled under protective materials, for example, inert hydrocarbons. The

such as propane. By way of example, after aluminum has been frictionally contacted with a columbium metal oxide layer, yttrium may be applied thereto under the protection of a hydrocarbonthen removed.

The rate earth metals may be in the form of mixtures,

such as misch metal. Combinations of other Group III dipped in a phosphoric acid bath. After the treatment with phosphoric acid, the article maybe washed with water and permitted to dry.

The following examples set forth preferred methods of carrying out the invention. They are furnished by wayof illustrations, tion.

. EXAMPLE I The surface of pure columbium was oxidizedby heating in air to ranges from 600 F. to 900 F., to form an oxide film thereon. The oxide film was rubbed with aluminum foil until an excess of aluminum was noted on theoxide film The article was then dipped in a bath of technical concentrated phosphoric acid. The article was maintained in the phosphoric acid bath during the reaction which was evidenced by the formation of hydrogen gas. After the evolution of hydrogen gas had discontinued, the article was removed, the'excess phosphoric acid removed, and the article cleaned. by washing with tap water, and permitted to dry.

and not as limitations to .the inveninert hydrocarbons may be one that readily volatilizes,

The article so treated was tested for its resistance. to

oxidation by heating to 1,600 F. in atmospheric oxygen which normally would produce catastrophic oxida- EXAMPLE 2 The same procedure is followed as set forth in Example 1, except that after the frictional application of aluminum foil, comminuted yttrium'powd'er dispersed in propane is sprayed on the oxide layer. The propane is volatilized and the article immediately dipped in a phosphoric acid bath.

EXAMPLE 3 The same procedure is employed as set'forth in Example 1, except that after the frictional application of aluminum foil, misch metal dispersed in propane is sprayed on the oxide layer. The article thereafter is dipped in a phosphoric acid bath.

There are many unusual advantages resulting from the protection of columbium in accordance with the foregoing procedure. Not only is the pure columbium metal protected against the catastrophic oxidation, at I temperatures above about 1,000 F., but the mechanical properties of the metal are preserved. Moreover, the surface of columbium is provided with an electrically insulative layer.

The process of the invention lends itself to. many new applications. The columbium metal with its good duc tility may be formed to the desired shape such as a turbine blade, reaction vessel, or die, and then subjected to the process described hereinabove, in order to pre- .any of the following claims, or the equivalent of such, be employed.

I claim:

1. In a process for providing a barrier on the surface of columbium articles, the steps comprising:

forming a columbium oxide layer on articles of columbium metal selected from the class consisting-of columbium and columbium base metal alloys by heating said articles in an oxygen containing atmo' sphere to temperatures in the range from about 600 F. to about l,200 F., at a point and for a time sufficient to form adherent film,

reacting said columbium oxide layer with at least one Group III metal in solid form, and

oxidizing said Group III metal.

2. In a process according to claim'l in which said Group III metal is selected from the classconsisting of aluminum, scandium, yttrium, and the rare earth metals. Y

3. ln a process according to. claim l in which said 5. In a processaccording to claim 1 in which said Group Ill metal is at least one rare earthmetal.

6. In a process according to claim 1 in which said oxidation of the Group lll metal is with phosphoric acid.

7. In a process for providing a barrier on the surface of columbium articles, the steps comprising:

forming a columbium oxide layer on articles of co lumbium metal selected from the class consisting of columbium and columbium base metal alloys by performed by treating Group III metal is selected from the class consisting of aluminum, scandium, yttrium, and the rare earth metals.

9. In a process according to claim 7 in which said Group Ill metal is aluminum.

10. In a process according to claim 7 in which said Group III metal is yttrium.

11. In a process according to claim 7 in which said v 6 Group III metal is at least one rareearth metal.

12. In a process according to claim 7 in which said Group III metal is oxidized by treating with phosphoric acid.

13. In a process for pro iding a barrier in the surface of columbium articles, the steps comprising:

forming a columbium oxide layer on articles of columbium metal selected from the class' consisting of columbium and columbium base metal alloys by heating said article to temperatures in the range from about 600 F. to about 900 F., in an oxygen containing atmosphere to a point and for a time sufficient to form an adherent oxide film, and reacting said oxide layer with a Group III metal in solid phase by mechanical contacts therebetween. 

2. In a process according to claim 1 in which said Group III metal is selected from the class consisting of aluminum, scandium, yttrium, and the rare earth metals.
 3. In a process according to claim 1 in which said Group III metal is aluminum.
 4. In a process according to claim 1 in which said Group III metal is yttrium.
 5. In a process according to claim 1 in which said Group III metal is at least one rare earth metal.
 6. In a process according to claim 1 in which said oxidation of the Group III metal is performed by treating with phosphoric acid.
 7. In a process for providing a barrier on the surface of columbium articles, the steps comprising: forming a columbium oxide layer on articles of columbium metal selected from the class consisting of columbium and columbium base metal alloys by heating said articles in an oxygen containing atmosphere to temperatures in the range from about 600* F. to about 900* F., at a point and for a time sufficient to form adherent film, reacting said columbium oxide layer with at least one Group III metal in solid form, and oxidizing said Group III metal.
 8. In a process according to claim 7 in which said Group III metal is selected from the class consisting of aluminum, scandium, yttrium, and the rare earth metals.
 9. In a process according to claim 7 in which said Group III metal is aluminum.
 10. In a process according to claim 7 in which said Group III metal is yttrium.
 11. In a process according to claim 7 in which said Group III metal is at least one rare earth metal.
 12. In a process according to claim 7 in which said Group III metal is oxidized by treating with phosphoric acid.
 13. In a process for providing a barrier in the surface of columbium articles, the steps comprising: forming a columbium oxide layer on articles of columbium metal selected from the class consisting of columbium and columbium base metal alloys by heating said article to temperatures in the range from about 600* F. to about 900* F., in an oxygen containing atmosphere to a point and for a time sufficient to form an adherent oxide film, and reacting said oxide layer with a Group III metal in solid phase by mechanical contacts therebetween. 